1. Field of the Invention
The present invention generally relates to an automatic copying machine which is arranged to copy the front surface of an original document onto the front surface of a copy paper, and the reverse surface of the original document onto the reverse surface of the copy paper which is already copied on the front surface thereof, and more particularly, to an automatic duplex copying machine for copying both surfaces of different original documents onto both surfaces of copy papers successively in such a manner that the front surface and the reverse surface of an original document are copied correspondingly onto the front surface and the reverse surface of a copy paper even when paper jamming takes place during the copying operation.
2. Description of the Prior Art
Generally, in order to copy onto both sides of a copy paper or a plurality of sheets of copy paper, the number of which is corresponding to a predetermined set number of copies (the set number of copies to be produced), the sheets are copied first on the front surfaces thereof, temporarily stored in an intermediate tray, and then copied onto the reverse surfaces thereof. In the automatic copying machine described above, in the case where copy papers happen to be jammed in the course of a copying operation onto the reverse surfaces thereof, the jammed papers are removed, resulting in a difference in the number of papers. In other words, the number of copy papers which are actually copied onto both surfaces thereof becomes smaller than the set number of copies to be produced. Noting the above fact, therefore, it has been so arranged in the prior art copying machine to detect the discordance or the difference in the number of copy papers copied on the front surfaces from copy papers copied on the reverse surfaces, thereby to obtain the insufficient number of copies generated because of an abnormal condition such as paper jamming during the copying operation onto the reverse surfaces of copy papers. When the number of copies is short, copying is carried out again onto the copy papers by the insufficient number of copies.
According to the above described prior art copying machine, however, a plurality of original documents having both surfaces printed should be copied onto respective both sides of copy papers with the employment of an automatic document feeder, and if the paper jamming takes place in the verso copying operation with respect to a particular original document, the recto copying operations are carried out more times than the verso copying operations. This is because the copying machine with the automatic document feeder is arranged first to carry out the recto copying operations successively by the set number of copies for each original document, and then to carry out the verso copying operations by the set number of copies for each original document after drawing out the recto-copied copy papers from the intermediate tray. Therefore, if the paper jamming or the like happens in the verso copying operation with respect to a halfway original document, the copy paper which should be copied with the verso of a coming original document is undesirably copied with the verso of an original document precedent to the coming original document, resulting in discordance of the copied surfaces of the original document and the copy paper.